main issues are that it can cause infections. The sides of my fingers are often red and swollen and painful if I bite them down too far or rip bits off the side. It can also push your teeth out a bit (I've basically undone all the good my brace did).

Like anything, it was the initial breaking of the habit that was important - first few days or so. The difficulty is that it was subconscious so I would find myself nibbling my nails without knowing how it had started. I'm told Stop n Grow works - makes sense because stuff tastes like shit and would definitely break the habit. I used the 'elastic band method': band on my wrist and every time I found myself chewing I'd flick it enough to sting a little. Sort of aversion therapy without the electric shocks. After a while it makes you conscious of the habit hence able to stop doing it. I also bought some decent nail clippers which I used regularly to keep the nails short and neat.

P.S. The elastic band method can be used for any habit you'd like to break.